Combined evaluation of LC3B puncta and HMGB1 expression predicts residual risk of relapse after adjuvant chemotherapy in breast cancer

Abstract

In spite of adjuvant chemotherapy, a significant fraction of patients with localized breast cancer (BC) relapse after optimal treatment. We determined the occurrence of cytoplasmic MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3B)-positive puncta, as well as the presence of nuclear HMGB1 (high mobility group box 1) in cancer cells within surgical BC specimens by immunohistochemistry, first in a test cohort (152 patients) and then in a validation cohort of localized BC patients who all received adjuvant anthracycline-based chemotherapy (1646 patients). Cytoplasmic LC3B+ puncta inversely correlated with the intensity of SQSTM1 staining, suggesting that a high percentage cells of LC3B+ puncta reflects increased autophagic flux. After setting optimal thresholds in the test cohort, cytoplasmic LC3B+ puncta and nuclear HMGB1 were scored as positive in 27.2% and 28.6% of the tumors, respectively, in the validation cohort, while 8.7% were considered as double positive. LC3B+ puncta or HMGB1 expression alone did not constitute independent prognostic factors for metastasis-free survival (MFS) in multivariate analyses. However, the combined positivity for LC3B+ puncta and nuclear HMGB1 constituted an independent prognostic factor significantly associated with prolonged MFS (hazard ratio: 0.49 95% confidence interval [0.26–0.89]; P = 0.02), and improved breast cancer specific survival (hazard ratio: 0.21 95% confidence interval [0.05–0.85]; P = 0.029). Subgroup analyses revealed that within patients with poor-prognosis BC, HMGB1+ LC3B+ double-positive tumors had a better prognosis than BC that lacked one or both of these markers. Altogether, these results suggest that the combined positivity for LC3B+ puncta and nuclear HMGB1 is a positive predictor for longer BC survival.